Why humans cannot draw circles
A perfect circle is the shape with constant curvature: every point exactly the same distance from the centre, turning at exactly the same rate the whole way round. That is trivial for a compass, which is a rigid arm pinned at one end, and close to impossible for you, because your drawing arm is not one rigid arm pinned at one end. It is several jointed segments, each with its own natural radius, handing off to one another as the stroke travels.
Draw from the wrist and you get an arc of roughly wrist radius. Draw from the elbow and you get a larger arc. Somewhere around the top and bottom of the stroke, control passes between joints, the effective radius changes, and the shape flattens. That is why almost every freehand circle comes out as a slight oval, and why the flat parts show up in the same places for most people.
What your score is actually measuring
The stroke you draw is fitted to the closest possible circle by least squares. This is worth stressing: you are not being compared to a circle we chose in advance, you are being compared to the best circle that could be drawn through your own points. You cannot game it by drawing somewhere unexpected or at an unusual size.
From that fit come three numbers. Roundness is the average distance your line strays from the ideal radius, and carries most of the weight. Closure measures how far your finishing point landed from your start, which catches the neat arc that simply stopped. Smoothness looks at how much the radius changes between consecutive points, which catches a shaky hand that happens to average out to roughly the right shape.
Those three can disagree, and the disagreement is informative. A careful ellipse scores well on closure and smoothness while roundness collapses. A trembling stroke does the reverse.
Why the numbers feel harsh
Deliberately. A naive accuracy score gives almost everything above ninety-five percent, because the average deviation of even a bad circle is small compared to its radius. The result is a number that cannot distinguish a good attempt from a poor one, which makes it worthless as something to chase.
So the deviation is amplified before it becomes a score. A careful freehand circle lands in the low nineties, a casual one in the seventies, and something genuinely wobbly drops into the fifties. The gaps between those are what make one more attempt feel worth it.
Some shapes, scored
The final number is sixty percent roundness, twenty percent closure and twenty percent smoothness. The clearest way to see what that weighting does is to feed the scorer shapes drawn exactly by a computer rather than by a hand, so the only thing being judged is the shape itself.
An oval ten percent narrower one way than the other scores 93.5. Squash it to twenty percent narrower and it falls to 86.3. A perfect circle that stops thirty degrees short of where it began scores 93.1: its roundness is still a flawless 100, and the unfinished gap alone costs it nearly seven points. On a circle with a 150-pixel radius, a one-pixel tremble either side of the line scores 95.4, because roundness barely notices it while smoothness drops to 84. A square, for comparison, scores 79.3 — about the same as an oval thirty percent narrower one way than the other, which gets 78.5.
Some strokes are refused rather than scored. Fewer than twelve points, a fitted radius under 40 pixels, or a stroke that sweeps less than 300 degrees around its own centre all get a message instead of a number, because there is nothing fair to measure. Stopping thirty degrees short costs you points; stopping more than sixty short costs you the attempt.
Reading your own drawing
The drawing is more useful than the number. While you draw, the score is refitted every few points, so you can watch it rise and fall. Once there is enough stroke to fit, a faint dashed circle appears behind it: that is the best circle through your own points, the one you are being measured against. Your line is coloured by how far each part strays from it, green where it sits on the dashed line and shading to red as it wanders off. The red stretches are where the next attempt should be different. Everything else already worked.
How to actually improve
Move from the shoulder, not the wrist. The shoulder has the longest reach and the most even arc, which is why life-drawing classes teach big loose circles from the shoulder before anything else. Draw larger than feels natural — error scales with radius, so a big circle forgives the same wobble that ruins a small one.
Go quickly and commit. A fast confident sweep uses ballistic movement, which your motor system plans in advance and executes without correction. A slow one uses continuous feedback, and every correction is a chance to wobble. This is the opposite of the instinct most people have, and it is the single change that moves scores most.
And practise the loop rather than the circle. Some artists trace the shape in the air a few times before touching the surface, letting the arm find the arc first. It looks like a superstition; it is really just motor priming, and it works.
If you enjoy this sort of thing, the reaction test and ten seconds measure two other narrow physical skills you did not know you had opinions about.
Questions people ask
What counts as a good score?
Anything over 90% is a genuinely good freehand circle and most people do not get there on their first few tries. The mid-eighties is a solid result. Above 97% is technical-drawing territory, and above 99% usually means a compass was involved.
How is the score calculated?
Your stroke is fitted to the closest possible circle using a least-squares fit, then measured three ways: roundness is how far your line strays from that ideal radius, closure is how near your finish landed to your start, and smoothness is how much the line wobbles point to point. Roundness carries most of the weight.
Why did my circle get rejected?
Four things are refused rather than scored: fewer than a dozen points, a shape too small to judge fairly, a stroke that never goes most of the way round, and anything that is effectively a straight line. Draw big, in one continuous stroke, all the way back to where you started.
Why can nobody draw a circle?
Because a circle demands constant curvature, and your arm cannot produce it. Drawing from the wrist or elbow traces an arc of whatever radius that joint happens to have, so the natural freehand shape is an oval. Getting a true circle means continuously correcting a movement your body wants to make differently.
Is the ranking based on other players?
No. Nothing you draw leaves your browser and there is no server collecting scores, so the ladder is a fixed set of thresholds rather than a live percentile. It is a description of the score, not a comparison against real people.
Does drawing slowly help?
Usually the opposite. Slow strokes give your hand more opportunity to wobble, which shows up in the smoothness score. One confident sweep tends to beat a careful crawl. If you take more than about nine seconds the result still counts, but it gets a small remark.